MEXICO CITY - Veteran television crime reporter Saul Diaz was interviewing witnesses to a murder in central Mexico City when his desk called: A mob was beating three police officers in a colonial-era town 30 miles south of the capital.

It was 6:20 p.m., Nov. 23. Diaz, a burly video-reporter for Mexico's TV Azteca network, and his driver, Guillermo Chavarria, jumped onto their Honda Shadow motorcycle. Skirting heavy traffic, they arrived at San Juan Ixtayopan at 7 p.m.

What Diaz found there shocked even him, a former paramedic who's covered riots, murders and kidnappings as a crime reporter. A mob of 700 people surrounded the three officers, who were tied up, bloody and half-conscious. Diaz began filming.

"People shouted to beat them more. Parents put children on their shoulders so they could see," Diaz recalled. He called it "the most horrible story I've covered" in his 11-year reporting career.

Then, at 8:30 p.m., the mob set two of the officers on fire.

"It was heartbreaking, and I was livid. As a paramedic, I felt powerless. They were still alive and breathing," Diaz remembered.

His tape of that horrific scene was played and replayed on news broadcasts in Mexico for days. Other reporters arrived at the town shortly after Diaz. They, too, recorded the officers' final, agonizing gasps.

Police, however, didn't arrive for another hour - three hours after the incident began. By that time, the third officer had been tied to a kiosk and doused with gasoline, but not yet set aflame. He was rescued.

Why it took police so long to respond remains unexplained. Some officials have blamed traffic and the road. Others say there weren't enough reinforcements on hand. Still others cite confusion.

Diaz scoffs. "They had plenty of time and the right equipment to get there fast, just like us," he said.

Diaz has spent his entire adult life involved in tragedy. During his four years as a paramedic, he confronted the pistol-wielding relatives of a heart attack victim who demanded that he resuscitate their patriarch, even though the man clearly had died. Another time, he recovered the severed arms and legs of a man who'd been struck by a train, in the vain hope they might be reattached.

The past year has been hectic. Last December, Diaz covered the stoning deaths of three people who were accused of stealing cattle and assaulting taxi drivers in San Pablo Oxtotepec, another town south of Mexico City. A month ago, he filmed police saving a thief whom a mob accosted in nearby San Lorenzo.

When the call came from his editor Nov. 23, Diaz was working on another crime, the mob-style murder of the owner of a dietary-supplement store who'd been gunned down as he sat in his car in the Mexico City neighborhood of Condesa.

Neither Diaz nor his editors knew any details, just that seven people had phoned the newsroom between 6 and 6:20 p.m. about a mob in San Juan Ixtayopan. Diaz learned only later that the besieged officers were members of the Federal Preventive Police, on a drug stakeout outside an elementary school. The crowd had pounced on them after they were accused of kidnapping children.

Diaz and his driver are prepared to move quickly. Their Honda, with a 750 cc engine, has special gears and high intensity lights. They wear padded suits, boots and helmets, and the driver has been trained to maintain high speeds while weaving in and out of traffic. The expectation: that they reach any crime scene in the city within 15 or 20 minutes.

Diaz remembers that the traffic that evening was terrible. They traveled on a main highway, then side streets. Seated behind his driver, Diaz couldn't see how fast they were going. The scenery was a blur.

The first thing Diaz saw 40 minutes later was the officers' overturned and shattered car, gasoline spilling. The crowd descended on him, many demanding that he videotape the scene "to show what happens to child kidnappers," others threatening to kill him, mistaking him for a police officer.

Diaz said time stood still as he explained that he was a reporter. Then adrenaline kicked in. Crawling on his knees, dodging kicks and people tugging at his equipment, he moved to 2 feet from where the officers were tied up.

"They were bloody and couldn't stand," he said.

At one point, the crowd tried electrocuting the officers with wires from a utility pole, but the wires weren't long enough.

Diaz and other reporters persuaded the crowd to let two of the officers call supervisors. "They're going to kill us. Please send help fast," officer Edgar Morelos, who survived, was recorded saying.

Diaz called a police delegation 8 miles away. People yanked the phone away. "If you don't get here in 15 minutes, we're going to kill them," a man shouted into the mouthpiece.

The crowd pulled Diaz by the hair. Some shouted for him to keep filming, others for him to shut off the camera. Some people threw firewood and paper at the blazing bodies to keep the fire going. Diaz could smell flesh and hair burning.

When the first police reinforcements arrived - 10 members of the capital's Immediate Reaction Team - the two officers, Victor Mireles Barrerra, 59, and Cristobal Bonilla Colin, 26, were dead, and the crowd was beginning to disperse, Diaz said.

So far, authorities have arrested 29 people, including four minors and two officers from the capital's Secretariat of Public Security, many of them identified from Diaz's footage. They're charged with homicide, attempted homicide, theft and destruction of property.

Diaz, the father of six children, has his own theory about responsibility in the deaths.

"Many of these towns have traditions that date back hundreds of years, and they enforce community justice, independent of constitutional law. I've seen authorities not intervene, saying, `Let them solve their own problems,'" he said. "But here, everyone is guilty: the crowd, witnesses, police and the government."

Still, Diaz believes that dignity and civility survive in Mexico City.

"Compared to other large violent cities, there are many places here where you can walk safely, in peace, and see beauty," he said. "I'm around noble and good people all day."